1. Field of the Invention
The present invention relates to a thermoplastic resin composition having excellent heat resistance, impact resistance, oil resistance and water resistance, and to a method for preparing the same. The composition of the present case can be widely utilized as a material for automobile parts, electrical, electronic and machine parts, industrial parts, and the like.
2. Description of the Prior Art
Polyamide resins, polyphenylene ether resins, aromatic polyester resins, polycarbonate resins, polyoxymethylene resins, ABS resins, polyarylene sulfide resins and polyarylate resins are used in many fields because of their excellent mechanical characteristics, heat resistance, chemical resistance and the like.
In recent years, various researches have been carried out with the intention of heightening the functions of products and decreasing the costs thereof, and above all, it has been attempted to utilize various features of plural plastics for the purpose of adding many functions to the products.
The polyamide resins are excellent in moldability, heat stability, wear resistance and solvent resistance, and thus they are employed in various kinds of molded articles. However, the polyamide resins have a high hygroscopicity, and therefore the dimensional stability thereof is poor, so that applications of these resins are limited at times.
On the other hand, the polyphenylene ether resins are excellent in mechanical properties, electrical properties and heat resistance, and what is better, they are also good in dimensional stability. Therefore, these resins are useful as raw material resins to be molded. However, they are inconveniently poor in workability, oil resistance and impact resistance. The aromatic polyester resins are excellent in mechanical properties, stiffness and strength, but poor in impact resistance and heat resistance. The polycarbonate resins are excellent in heat resistance, mechanical properties and impact resistance but poor in chemical resistance. Polyoxymethylene resins are excellent in dimensional stability and mechanical properties but poor in impact resistance. The ABS resins are excellent in impact resistance but poor in chemical resistance. The polyarylene sulfide resins are excellent in heat resistance and flame retardance but poor in ductility and thus brittle. The polyarylate resins are excellent in heat resistance but disadvantageously poor in impact resistance.
Accordingly, it can be presumed that if the polyamide resin (I) is blended with one or more resins (II) selected from the group consisting of the polyphenylene ether resins, the aromatic polyester resins, the polycarbonate resins, the polyoxymethylene resins, the ABS resins, the polyarylene sulfides resins and the polyarylate resins, a resin composition can be obtained in which the features inherent in the polyamide resin (I) are maintained and the drawbacks thereof are eliminated and to which the features of the other resin (II) are added.
For example, Japanese Patent Publication No. 45-997 discloses that the polyamide resin is blended with the polyphenylene ether resin in order to improve the oil resistance and the workability of the latter resin, but the compatibility of the polyphenylene ether resin with the polyamide resin is very bad. Accordingly, the resulting resin composition has poor mechanical properties (particularly when the content of the polyamide is in excess of 20% by weight, the mechanical properties are noticeably poor). In addition, the molded articles of such a blend obtained by injection molding exhibit a delamination phenomenon, with the result that any preferable molded articles cannot be obtained.
As relatively excellent techniques for preventing the above-mentioned delamination phenomenon, there are a process described in Japanese Laid-open Patent Publication No. 60-36150 in which a copolymer comprising a styrene compound and an .alpha.,.beta.-unsaturated dicarboxylic anhydride is used as a compatibilizing agent, and a process described in Japanese Laid-open Patent Publication Nos. 60-260649 and 62-27456 in which a copolymer comprising ethylene or a styrene compound and an unsaturated compound containing an epoxy group is used as the compatibilizing agent, and a process described in Japanese Laid-open Patent Publication No. 64-48846 in which a multi-phase structure thermoplastic resin is used as the compatibilizing agent. The above-mentioned first process has the drawback that bubbles are formed probably owing to the decomposition of the dicarboxylic acid in a step of heating/molding, and in the above-mentioned second and third processes, the improvement effect of impact resistance is still insufficient.
Moreover, in Japanese Patent Publication Nos. 47-19101 and 47-24465 and Japanese Laid-open Patent Publication Nos. 48-56742, 49-114661, 56-34754 and 57-49657, some attempts have been made to solve problems attributed to the combination of the polyamide resin and the polyester resin by changing blend compositions of these resins or by additionally using a fibrous reinforcing agent or an inorganic filler as an additive in compliance with the intended purposes. However, molded articles obtained by these procedures have poor mechanical properties, and for example, the delamination phenomenon tends to occur in these articles.
Furthermore, Japanese Laid-open Patent Publication Nos. 62-277462 and 62-283146 disclose techniques which use an ethylene copolymer containing an epoxy group and an ethylene copolymer containing an acid anhydride together in order to improve the affinity between the polyamide resin and the polyacrylate resin. These polymers are effective to heighten impact strength, but they have the disadvantage that stiffness and heat resistance of a composition thereof are liable to fall off.
The other resins are also tried to improve physical properties by various combinations with the polyamide resin. However, they are different from the polyamide resin in chemical structure, and for this reason, no affinity is present therebetween, so that features of the respective resins are scarcely utilized.